This invention relates to optical modulators, e.g. for optical communications systems, and in particular to modulation exhibiting the quantum confined Stark effect (QCSE). The invention further relates to a method of fabricating such modulators.
Electro-optic modulators employing the quantum confined Stark effect (QCSE) are of considerable interest as potential key components in optical communications systems. A description of a QCSE device is given for example by D. A. B. Miller et al in Phys. Rev., 1985, B32, p1043. The effect arises in a quantum well structure when an electric field is applied perpendicular to the plane of the quantum wells. This alters the confined energy states and shifts the absorption resonance to lower energy thus providing the basis for optical modulations and switches. In current QCSE devices the quantum wells have symmetric barriers. We have found that this structure provides a device in which the electrically induced shift of the absorption peak to longer wavelength is proportional to the sequence of the applied electric field. We have also found that the large wavelength shifts associated with higher applied fields are accompanied by a decrease in the light or intensity of the absorption peak. This effect limits the efficiency of the device.
In addition current devices suffer from the restriction that the wavelength shift is only towards longer wavelengths and is independent of the polarity or direction of the applied field.
The object of the invention is to provide an improved optical modulator.